An aftermarket air cleaner won't void your warranty, and it's cheap. It won't do much, but they do make for a little more power, and better economy. It's CHEAP, easy to install, and they should last forever if you take care of them. All you have to do is clean it, and put oil on it (special oil they make for it, not just motor oil). The K&N air filters are the best, and they make them for almost anything. Should be about $30, it will be a good investment. I put one in my truck, and it made a little bit of a difference. I don't want to spend $150 for the cold air intake pipe, it's a waste of $$$.